Indeed the onboard soundcards are of relatively high quality now. But if your question is if it is better with a sound card. The answer is yes. Onboard soundcards still can not match a dedicated soundcard in any way. It all comes down to your preferences in sound quality. I'd say on board cards are very well suited for the general gaming and multimedia experiences. However, if you are into listening to music and also invest in high quality headphones for example, you will get much more from a dedicated soundcard. In this scenario i would invest in a usb external card to get it away from the noise interfierence inside the case.
But as I said, if you are the general gamer or multimedia guy and do not demand the highest sound quality on...